Let, Ages of father and Son today is “7A” and “3A” years correspondingly.
Then, 5 years, then we get,
{ (7A + 5)/(3A + 5) }= (2/1)
A = 5
Present age of father is 35 years.
Present age of son is 15 years.
At the time of son’s birth, father have been (35-15) = 20 years.